A planet moves around the sun. At a given point P, it is closed from the sun at a distance  d₁ and has a speed v₁ . At another point Q. when it is farthest from the sun at a distance d₂, its speed will be : 

\(\frac{d_1 v_1}{d_2}\)

According to law of conservation of angular momentum :

\(m v_1 d_1 = m v_2 d_2\)

\(v_2 = \frac{d_1 v_1}{d_2}\)